Adjustable blade propellers have long been known. These propellers can be divided into two main types, one type with which each blade can be adjusted individually, and another type with which all blades are adjusted commonly in one single movement. One advantage with the latter type of propeller is that it eliminates the need to bring the individual setting of a blade into agreement with the settings of the remaining blades, which can be difficult to achieve and which may result in differences in blade settings.
The inventive propeller lies within this latter type of propeller, i.e. a propeller with which the propeller blades can be adjusted in unison.
Adjustable blade propellers of this kind are described and illustrated in U.S. Pat. Nos. 813,074, 2,574,951, 5,232,345, 2,953,208, 3,403,735, 3,308,889, for instance. A common feature of the propeller constructions described in these publications is that common or unison adjustment of the blades is made to a completely optional setting within the limits given, i.e. the blades can be adjusted to different settings smoothly and continuously. The blades are locked in their new settings, subsequent to this adjustment. This procedure has several drawbacks. Firstly, it is necessary to be able to read or determine the blade setting, so as to establish whether or not the blade has been adjusted to the angle intended. There is also the risk of deviation between the blade setting intended and the blade setting achieved. Furthermore, it is necessary to rely upon force-bound locking of the blades when practicing this continuous blade adjustment principle. This force-bound locking of the blades can result in a change in the blade setting, or may require the application of locking forces of such great magnitude as to cause dismantling and fitting operations in respect of the adjustment more difficult to achieve and induce higher tensions in the material. There is also the risk of a heavily tightened locking device becoming loose in the passage of time, due to vibration and other forces, so as to disturb the blade settings. As a result, a number of the earlier constructions have become highly complicated.
EP 0 300 252 teaches a blade adjuster with which the blades can be adjusted to distinct settings in unison. The arrangement is, however, relatively complicated and involves the conversion of a torsional adjustment movement to an axial adjustment movement of a rod that extends to each propeller blade, through the medium of nuts and spindles. The axial movement of the rod is then converted to rotational movement of respective blades through the medium of a pin carried by the rod and co-acting with a guide groove or channel in the blade root.